This invention relates to a light amount correction method and the apparatus therefor which corrects for variations in the light amount caused by thermal or structual changes in a semiconductor light source which is used in an image output system.
A semiconductor light source such as a light emitting diode is widely used as the light source for image output systems which expose photographic films and output images because semiconductor light sources are advantageous in durability and cost. Semiconductor light sources, however, suffer defects in that thermal conditions significantly influence emission efficiency as well as spectral characteristics. There have been proposed various methods for correcting for such fluctuations. The most widely used method comprises the steps of detecting the temperature of a light source and compensating for the change, but the measurement of the temperature in the light source per se presents considerable difficulties, which often makes accurate correction almost impossible. It is also difficult to correct changes in light amount caused by chronological changes in the light source or to compensate for the changes in light amount occurring as the light advances from the semiconductor chip to the photographic material. The demand for an apparatus which can correct for all of those fluctuations is therefore keenly felt.
The semiconductor light source is also defective in that the amount of exposure widely fluctuates because of the synergistic effect with the spectral sensitivity of a photographic material such as photographic films. Various corrective methods have been contrived to compensate for such thermal fluctuations. For example, the temperature of a semiconductor light source is kept constant by means of a heater according to one of the prior art methods. Such a method is, however, not desirable because it does not take into account the characteristics of the photographic material at all, and the life of the light source is unavoidably reduced as it is constantly used at a high temperature, and additional energy is needed for controlling the temperature.